2.0 Analysis 2.1 Introduction The investigation did not reveal any mechanical difficulties with the aircraft's engines nor with the aircraft's primary and secondary flight controls. This analysis will concentrate on the aircraft's altimeters, the AWOS altimeter setting, weather, and pilot decision making, all of which could have contributed to the occurrence. Additionally, survival issues will be discussed. 2.2 Aircraft Altimeters The last recorded radar transponder information places the aircraft approximately 3.1 nm from the Big Trout Lake radar site, which corresponds to the approximate distance to the initial impact location. Consequently, the last blind encoding altimeter transponder transmission received by the Big Trout Lake radar source likely occurred immediately prior to the aircraft hitting the ice surface of the lake. The last recorded transponder transmission received from the aircraft was from 710 feet asl. Because the known elevation of the surface of the lake is 690 feet asl, the blind encoding altimeter and the pitot static system it was using were likely functioning correctly. Additionally, because the blind encoding altimeter uses the first officer's pitot static system as its source, it is likely that the first officer's pitot static system was also functioning correctly. The first officer's altimeter performed within limits during post-occurrence testing. Additionally, because its pitot static system was likely functioning correctly, the accuracy of its altitude reading would be solely dependent on the accuracy of its subscale setting. That altimeter setting of 29.96 inches of mercury was obtained from the Big Trout Lake AWOS; consequently, the accuracy of the altitude reading being used by the first officer was solely dependent on the accuracy of the Big Trout Lake AWOS altimeter setting. Additionally, because neither the captain nor the first officer noted any discrepancy between their respective altimeters during their flight, the accuracy of the captain's altimeter was also determined solely by the Big Trout Lake altimeter setting as transmitted to the crew. 2.3 Automated Weather Observation System Calculations performed by the barometric specialist demonstrated that a setting of 29.96 would have produced an accurate altimeter reading at the time of the occurrence. Additionally, the AWOS fail- safe system did not activate, and the system was found to be functioning within allowable tolerances when tested against the regional standard. Therefore, it can be concluded that the AWOS measured and transmitted a valid altimeter setting of 29.96, which was properly set by the crew. Thus, the voice transmission of the AWOS at the time of the approach into Big Trout Lake was accurate. The discrepancy reported by other Bearskin crew at Big Trout Lake on the day of the occurrence could not be resolved. However, the discrepancy could have resulted in part from the airport elevation difference of 39 feet between the actual elevation and that found in the Canada Flight Supplement and GPS data base. When this crew set the transmitted Big Trout Lake AWOS altimeter setting on the ground, their altimeters would have read 777 feet, the correct altitude of Big Trout Lake Airport published in the Company Approach Chart, instead of the published 738 feet in the Canada Flight Supplement dated 08 December 1994. Although the discrepancy could not be fully explained, another carrier that had landed at Big Trout Lake at the time of the occurrence did not report any altimeter setting problems while using the AWOS setting. 2.4 Decision Making on Approach When the captain initially briefed the first officer for the instrument approach into Big Trout Lake, he noted that the only approach chart provided was in a binder and could not be readily removed. The captain accepted this condition, and consequently, to consult the chart during the approach, the captain had to hold the binder in his lap and look down to read the information. In addition, the chart was not readily accessible to the first officer. The crew descended to 150 feet agl approximately 4.5 miles from the end of the landing runway and maintained 200 to 300 feet agl for some 50 seconds prior to impact. Given the weather conditions of one mile visibility in snow that were reported by the crew, and the monochromatic appearance of the snow-covered surface of the lake, the crew's decision to continue to fly visually at this altitude exposed the crew to the risk of experiencing whiteout conditions. The captain was aware of the danger, and intended to revert to an instrument approach if whiteout were encountered. Although the decision to fly close to the lake surface reduced the margin of safety and the time available to react to any loss of situational awareness in whiteout conditions, the decision did not contravene ANOs or the company SOPs. This decision also caused an increase in the crew's stress and workload during the final approach phase, in that the crew were faced with maintaining terrain clearance visually at low level in adverse weather conditions. Thus, the crew had increased the likelihood of narrowing their attention to the primary task, that of maintaining visual terrain clearance, and to the most noticeable information source, the surrounding terrain. They had increased the likelihood of missing or discounting critical information provided by the altimeter and vertical speed indicator, without any awareness of doing so. Thus the crew's decision increased the possibility of the loss of situational awareness in whiteout. Because the radalt was not serviceable, it was not used by the crew as a warning device. The radalt setting of 1,050 feet, as observed by the investigators, is consistent with the crew's statement that they had not used the radalt. After the aircraft crossed the last chain of islands on track, about 3 1/2 miles from the runway, the Air Traffic Services radar data indicated that the aircraft was about 300 feet agl and was descending at more than 1,200 feet per minute. The first officer, who was flying the aircraft, did not stop the descent. Both his altimeter and vertical speed indicators were functioning accurately; however, it is unlikely that he was using them for altitude guidance. It is probable that he had unknowingly narrowed his attention to outside references for terrain clearance because of the stress and high workload of the low- level, visual approach. At this distance from the runway, the aircraft was over a wide expanse of lake, with the nearest shoreline in excess of a mile away. Thus, the visual cues required to maintain terrain clearance were beyond the one mile visibility reported by the crew. The absence of visual cues placed the crew in whiteout conditions. Because of a lack of visual altitude references in whiteout, it is unlikely that the first officer realized that he was ignoring instrument indications and that he was allowing the aircraft to descend into the terrain. Consequently, it is likely that the first officer lost situational awareness in whiteout conditions and was unable to take effective action. The captain had become concerned about the reducing visibility as they flew towards the airport, and decided to conduct an instrument approach. He did not instruct the first officer to begin a missed approach, but instead looked at the company approach chart in order to rebrief the first officer on approach information. After he consulted the chart, he looked up and observed that the altimeter was indicating a descent through 1,000 feet asl. His direction to the first officer was the non-specific command, Watch your altitude. Because of the low altitude of the aircraft and the high rate of descent, the first officer did not have time to assimilate and respond to the instruction. Consequently, the lack of timely action by the crew, when the first officer lost situational awareness in whiteout conditions, resulted in the aircraft descending into the terrain under controlled flight. As noted, the radar altimeter was not serviceable and consequently was not used by the crew as a warning device. A GPWS, if installed and operable, would have provided constant warnings and cues to the crew of their proximity to the terrain. 2.5 Survival Issues 2.5.1 ELT Although the posted instructions for the ELT met the regulatory requirement, they were difficult for passengers to understand in a stressful situation under harsh environmental conditions. In particular, the passengers could not see that they had indeed activated the switch, and they did not understand that the ELT would not emit an audible sound and only be transmitted on a radio frequency. 2.5.2 First Aid Kit Although the first aid kit met the regulatory requirement, its contents were inadequate to deal with the type of injuries sustained in this accident. Under the harsh environmental conditions to which the passengers were exposed, their chances of surviving for an extended period were greatly reduced. 2.5.3 Survival Kit The company was exempted from the need to carry sleeping bags in accordance with the Transport Canada approved Company Operations Manual. The company, however, had included foil-type survival blankets in a small kit in the aircraft. These foil blankets were critical in the reduction of hypothermia in the two most critically injured survivors. The lack of sleeping bags made it impossible to prevent hypothermia and might have resulted in more serious injury or death if rescue had been delayed. 2.5.4 Seat-Belt Attachment Fittings The four seat-belt attachment fittings were tested and found to meet the required standard. Therefore, it is probable that the three that failed during the impact broke because the force of the impact exceeded the design limit of 1,500 pounds. Consequently, the failure of seat-belt attachment fittings in this survivable accident may indicate that the limit is set too low. 3.0 Conclusions 3.1 Findings The crew was certified, trained, and qualified for the flight in accordance with existing regulations. The airport elevation listed in the Canada Flight Supplement dated 08 December 1994 was incorrect and was 39 feet lower than the correct airport elevation of 777 feet shown on the Company Approach chart. The aircraft altimeters were serviceable and set to the correct altimeter setting as reported on the AWOS. The AWOS was transmitting the correct visibility at the airport and an erroneous sky condition report. However, operation into Big Trout Lake was based on the ceiling and flight visibility as reported by the occurrence crew. The occurrence crew reported the visibility as one mile. The decision to fly visually at low level over the lake surface in one mile visibility increased the crew's stress and workload and exposed the crew to the risk of experiencing whiteout conditions; however, the decision did not contravene ANOs or company SOPs. The first officer unknowingly missed critical altitude information when he lost situational awareness in whiteout conditions. The crew did not react in a timely manner when whiteout conditions were encountered. The instructions for operating the ELT were confusing to the passengers. The lack of sleeping bags on board the aircraft, as permitted by the operating certificate, exposed the most critically injured survivors to hypothermia. The foil blankets provided in the aircraft reduced the effects of hypothermia in the most critically injured survivors. Three seat-belt attachment fittings failed in overload; the attachments met design specifications for strength. The first aid kit met the standard required by regulations but was inadequate for the type of injuries sustained by the survivors. The aircraft's radar altimeter was not serviceable. The aircraft was not equipped with a GPWS, nor was one required by regulation. The captain accepted an approach chart location that resulted in the only available approach chart not being readily accessible by either crew member. The company SOPs for the Beech A100 provided minimal guidance with regard to approach procedures. 3.2 Causes While the crew were manoeuvring the aircraft to land and attempting to maintain visual flying conditions in reduced visibility, their workload was such that they missed, or unknowingly discounted, critical information provided by the altimeters and vertical speed indicators. Contributing factors were the whiteout conditions and the crew's decision to fly a visual approach at low altitude over an area where visual cues were minimal and visibility was reduced. 4.0 Safety Action 4.1 Action Taken 4.1.1 Airport Elevation Subsequent to this occurrence, the Canada Flight Supplement was amended to indicate the airport elevation of Big Trout Lake as 777 feet asl. 4.1.2 Visibility Requirement in Uncontrolled Airspace In the proposed Canadian Aviation Regulations (CARs), the visibility requirement for aircraft operating under visual flight rules in uncontrolled airspace below 1,000 feet agl will be increased to two miles from the current one mile requirement. However, there will be provisions for Transport Canada (TC) to allow commercial operators to operate aircraft at lower visibilities provided that certain pilot training and aircraft equipment criteria are met. 4.1.3 Operating Instruction for ELTs In this occurrence, the passengers had difficulty operating the ELT. A TSB Aviation Safety Advisory was forwarded to Transport Canada regarding the need for the placarding of clear instructions for the use of ELTs, with the suggestion that this requirement be considered in the new regulations. 4.1.4 Ground Proximity Warning System (GPWS) Canadian regulations require only commercially operated, large turbo-jet powered aircraft (capable of carrying 10 or more passengers and with 15,000 kg or greater maximum certified take-off weight) to have GPWS installed. In the United States, all turbine powered (turbo-jet and turbo-prop) aeroplanes with 10 or more seats, notwithstanding their weight, require an operating GPWS. The aircraft in this occurrence, the Beechcraft A100, is certified for more than 10 seats; however, the Canadian regulation for GPWS is limited to turbo-jet powered aircraft only. The Board believes that the increased level of safety provided by GPWS should not be related to an aircraft's type of propulsion; rather the requirement for GPWS installation should be based on the role of the aircraft and its passenger-carrying capacity. Therefore, the Board previously recommended that: The Department of Transport require the installation of GPWS on all turbine-powered IFR- approved commuter and airline aircraft capable of carrying 10 or more passengers. Transport Canada replied that it would submit the GPWS issue to the Canadian Aviation Regulation Advisory Council (CARAC). The CARAC is establishing a sub-working group to look into safety systems, such as GPWS, traffic collision avoidance systems, and windshear avoiding systems. 4.2 Action Required 4.2.1 Post-Accident Survivability As evidenced in this occurrence, accident survival can depend to a large extent on post-crash conditions. Notwithstanding that this operator had complied with all regulations, the first aid kit on board the aircraft was not adequate to deal with the injuries to the passengers, some survivors suffered from hypothermia as a result of insufficient protection from the elements, and the passengers had difficulty following the instructions for post-crash use of the ELT. The issue of post-accident survivability has been an ongoing concern in commercial aviation. In 1986, following a PA-31 accident, the predecessor to the TSB, the Canadian Aviation Safety Board (CASB), expressed concern about the lack of survival equipment on small commercial passenger-carrying aircraft during winter operations, and recommended that: The Department of Transport, having due regard to space and weight limitations while benefitting from advances in available lightweight materials: a) prescribe a minimum list of survival equipment suitable for post-accident winter conditions; and b) require the carriage of prescribed survival equipment on aircraft operating during the winter on passenger-carrying flights under the provisions of Air Navigation Order Series VII, Numbers 3 and 6.